1. Field of the Invention
The present invention relates to absorption refrigeration systems and, more specifically, to such systems using ammonia as the refrigerant and water as the absorbent.
2. Description of the Prior Art
Absorption refrigeration systems are well known in the art and typically comprise a generator, a condenser, an evaporator and an absorber interconnected to provide paths of flow for the refrigerant and the absorbent. The solution of refrigerant and absorbent in the generator is heated to expel refrigerant vapor therefrom. The expelled vapor is then delivered to the condenser where it is condensed to a liquid by transfer of its heat of vaporization to an ambient medium at a lower temperature. The liquid refrigerant from the condenser is delivered to the evaporator where it evaporates at a relatively low pressure. The evaporation of refrigerant at the low pressure and temperature produces the refrigerating effect.
The relatively hot absorbent from which the refrigerant has been expelled in the generator (absorbent weak in refrigerant) is then cooled and delivered to the absorber. The cool absorbent weakened refrigerant in the absorber has a high affinity for refrigerant vapor and absorbs vapor from the evaporator in open communication therewith to maintain the relatively low pressure and temperature in the evaporator.
The absorbent into which the refrigerant vapor has been absorbed (solution strong in refrigerant) is then delivered back to the generator by a pump, or other means, and the cycle is repeated. Thus, the generator and condenser operate at a relatively high pressure while the evaporator and absorber operate at a relatively lower pressure. Restricting means are typically provided between the high and low pressure sides of the system which together with the solution pump maintain the difference in the pressures in the two sides of the system.
The use of heat exchangers, analyzers and rectifiers is also well known in absorption refrigeration systems to improve their efficiency. The heat exchanger transfers heat between the relatively hot absorbent weakened refrigerant flowing from the generator to the absorber and the relatively cool absorbent strong in refrigerant flowing from the absorber to the generator. The analyzer directly contacts the relatively cool absorbent strong in refrigerant in counter-flow with the relatively hot refrigerant vapor flowing from the generator to the condenser to separate liquid absorbent from the expelled refrigerant vapor to improve the quality of the refrigerant vapor entering the condenser. The rectifier transfers heat from the refrigerant vapor exiting the analyzer to a cooler solution in a heat exchanger to further reduce the amount of refrigerant vapor delivered to the condenser and again increase the quality of refrigerant vapor entering the condenser.
Absorption-type refrigeration systems accomplish cooling effects in a comparable manner to that described for the typical compression-type refrigeration system. The evaporator, condenser and throttling device are substantially similar in the two systems. However, a major distinction between the two systems is in the method used to increase refrigerant pressure between the condenser and the evaporator. In the compression-type system, the increase in pressure is accomplished by a mechanical means, namely the compressor. In the absorption-type system, the increase in pressure is brought about by means of heating an absorbent/refrigerant fluid, such as a water/ammonia mixture. The absorption refrigeration system is based upon the phenomenon of the absorption of ammonia vapor by water at lower temperatures and the expulsion of ammonia vapor when the water/ammonia mixture is heated.
The absorption refrigeration system has certain advantages over compression-type refrigeration systems. For example, the typical compressor used in compression-type systems has a number of moving mechanical parts and is somewhat noisy. The absorption refrigeration system, lacking the compressor, significantly reduces the noise level of the system. Maintenance requirements are also reduced, since there are no moving compressor parts to wear out or require regular maintenance.
A number of industries could benefit from the use of absorption-type refrigeration systems, except for limitations primarily dealing with the generator or primary heat source for the generator used in such systems. In the part, the primary heat source was usually provided by steam, gas burners, or electrical resistance heaters. For example, U.S. Pat. No. 4,914,919 shows an absorption refrigeration system operated by a heating cartridge from at least one electric current source or by a gas burner. Similarly, U.S. Pat. No. 4,487,030 shows another absorption refrigeration system which is operated by electrical resistance heaters or by flammable gas burners.
The practical use of these prior art absorption refrigeration systems was significantly limited due to several disadvantages associated with such heat sources used by the generator. In particular, the overall system efficiency of most of these prior art systems which used relatively inefficient generator heat sources was appropriately low in comparison to the system efficiency of most non-absorption-type refrigeration systems. In addition, most of the heating sources used by the generator in these prior art absorption systems required frequent and costly maintenance.
One industry which is in need of an absorption refrigeration system of low cost and maintenance and increased efficiency is the fishing industry, for example, shrimp boats. These boats take in fresh catch which could, preferentially, be flash-frozen on the boat while on the water, and stored in a refrigerated hold of the boat if an adequate refrigeration system was available at an economical cost.
A need exists to provide an absorption refrigeration system for this and other uses which provides increased efficiency of operation while decreasing the amount of routine maintenance which must be performed on the system.
A need exists to provide such an absorption refrigeration system which is more thermally efficient and yet which is cost effective and competitive with existing compression refrigeration systems in price.
Accordingly, it is an object of the present invention to provide a high efficiency absorption refrigeration system and method which is cost effective and low in maintenance.